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Table 1 Current overview of MAM functions and comparison of how they operate in mammalian and yeast model systems

From: Of yeast, mice and men: MAMs come in two flavors

Function (including brief description) Mammalian-specific characteristics Yeast-specific characteristics
Phosphatidylserine (PS) Transfer: PS is made on the ER, but transferred to mitochondria for the production of phosphatidylethanolamine (PE) [4, 84] PS transfer occurs on a triple contact site between ER, OMM and IMM [25–27], requires ATP [90] and cytosolic Ca2+ [91]. PS transfer occurs at ER mitochondria contact sites [96], but does not require ATP [17, 97]. PS transfer is not obligatory, since Psd2p can replace mitochondrial PE production [98, 99].
Role of sterols on MAM MAM has lipid raft characteristics and is marked with caveolin [116–122]. ORP5 and ORP8 form a protein bridge with mitochondrial PTPIP51 [130]. No raft characteristics known as of today [123].
Ca2+ handling at the MAM; mitochondria receive Ca2+ from the ER upon formation of a Ca2+ microdomain [155–163] Mitochondria import Ca2+ via the mitochondrial Ca2+ uniporter (MCU) [148–150]. Ca2+ is required for mitochondrial dehydrogenases [132] and respiration [133]. No MCU present [148–150]. Ca2+ is required for mitochondrial dehydrogenases [151]; increase of Ca2+ in the cytoplasm boosts mitochondrial respiration [194].
MAM Ca2+ signaling in apoptosis Massive MAM Ca2+ transfer accelerates apoptosis [39, 192]. Ca2+ is released from the ER [193].
ER chaperones on the MAM ER chaperones on the MAM control MAM Ca2+ transfer and cytosolic Ca2+ waves [180–188]. None detected.
Currently known MAM tethers or proteins regulating MAM tethering PACS-2 [38, 40], mitofusin-2 [42–45], BAP31/Fis1 (ARCosome) [41], IP3R/VDAC/Grp75 [73], PTPIP51/VAPB [74–76] PERK [65, 66] ERMES [18–20], EMC [34]
MAM and mitochondrial fission Drp1 oligomerizes on MAM to mediate mitochondria fission [15] Drp1 oligomerizes on MAM to mediate mitochondria fission [15]
MAM as point of origin for autophagy MAM is material for isolation membrane [16]. Implicated MAM proteins are calnexin, Drp1, FUNDC1 [220], Rab32, syntaxin-17 [222, 223], PACS-2, mitofusin-2 [16] ERMES mutants show no defect in Atg8p recruitment, but are defective in mitophagy and lipid supply for phagophore formation [22, 224]
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